The invention relates to solar energy collectors and, more particularly, to recirculating natural convection solar energy collectors.
The concept of utilizing the sun as a source of energy is an old and well known concept. While this is an old and well known concept, interest in this field has been somewhat limited until the recent energy crisis. The recent energy crisis has generated a great deal of activity in the field of solar energy and many different types of solar collectors have been developed recently and are now available on the market. Of course, various different types of solar collectors were developed and marketed prior to the energy crisis.
In a considerable number of these prior art solar collectors, a flowing liquid is in thermal contact with an absorber which absorbs the heat from the sun. The flowing liquid absorbs heat from the absorber of the collector and flows from the collector to a point where the heat is utilized. The liquid is then pumped back to the collector where it is again in thermal contact with the absorber of the collector and is again heated. In this prior art type of collector the liquid, which may be water, may merely flow over the top of the absorber plate. The water is heated as it flows over the absorber and the temperature of the water is reduced at its point of use and its temperature again raised as it flows back over the collectors. There are, of course, many variations of this type of collector. For example, a black dye has been added to the water in some prior art systems and in others liquids other than water are used. In still other variations, the liquid flows through pipes or closed channels that are integral with the associated plate.
Another type of prior solar collector that has been developed is commonly called a focusing collector. Focusing collectors have some means of focusing the sun's rays on the absorber of the collector. For example, many of the prior art focusing collectors use a generally parabolic shaped focusing element. In such systems, the absorber is generally a pipe containing a flowing liquid.
In addition to the two common types of prior art solar collectors described above, a few solar collectors in which the air in the collector is heated by the absorber have been devised. In such systems, the air flows past the absorber and is heated. The air with its thermal energy is delivered to its point of use where the heat may be extracted. Many of these prior art air systems use a blower to move the air. In a few other such air systems, the natural convection currents caused by the heating and cooling of the air is relied upon to circulate the air in the collector. These air type solar collectors offer some advantages over collectors utilizing fluids. For example, a minimum of corrosion resistant material is needed in an air type collector and generally these air type collectors are generally simpler in design and, therefore, less expensive than the conventional liquid type collectors. While such air type collectors have been designed, all of the prior art air type collectors of which the applicant has knowledge have complex absorber plate arrangements, or have absorber plate arrangements that tend to reduce the air flow rate in the collector. Examples of such prior art air type solar collectors are disclosed in U.S. Pat. Nos. 2,553,073; 3,875,925, and 3,939,818.
The solar energy collectors of this invention are air flow type collectors that are so designed as to maximize air flow in the collector by natural convection. Further, the solar collectors of this invention are relatively simple in design and, therefore, relatively inexpensive to construct.